Inhibition of Mild Steel Corrosion by 4-benzyl-1-(4-oxo-4-phenylbutanoyl)thiosemicarbazide: Gravimetrical, Adsorption and Theoretical Studies

Round 1

Reviewer 1 Report

Author Response

Dear Sir,

Thank you for your useful comments and suggestions.

Future studies will cover the DC and AC electrochemical methods. This work represents an optimization study for new corrosion inhibitors, hence further studies will be conducted in the future.   From the present study, we found that the synthesized corrosion inhibitor has promising protective efficiency for mild steel in a corrosive environment.

Thank you

Best regards

Reviewer 2 Report

The submitted manuscript is a sound work but needs some improvement to increase the impact and value. While the inhibitor compound appears to display promising protective qualities for mild steel in 1M HCl, a relatively harsh environment, it is difficult to tell its value as there is no comparison to other compounds, just some references to their own work in the literature. Also, while the data is sound there is no surface analysis or even optical or electron microscopy images to indicate the level of protection or pitting. 

In detail:

Abstract: The abstract sums up the work well, although some details in the final sentences are needed: 'Quantum chemical calculations based on the DFT calculations were conducted on BTO. Both experimental and theoretical findings in the current investigation are in excellent harmony.'

Introduction: This is mostly well written, however line 37-39 mentions 'metallic surface' 4 times in the one sentence, this could be reduced, such as: '...complexes with metallic surface utilizing the active sites, and these metallic complexes occupy a significant surface area, therefore coating the metallic surface and shielding it from acidic solutions.'

Materials and Methods: Mostly clear, however it is not clear in 2.2 if all weight loss experiments are repeated 3 times, or just the temperature experiments. Also, Section 2.4, was DFT calculated in gas or aqueous phase?

Results: The presentation of CR and IE graphs shows smoothed curves. Smoothed curves should not be used to present this type of data as it gives a false impression of the trends, for instance there is no proof that there is a minimum in corrosion rate somewhere between 5 and 10 hours for 100, 200, 300 and 400 ppm. Also, since IE is calculated directly from CR, how can the peak in IE not coincide with the minimum in CR for 100ppm? Straight lines should always be used to connect this type of data. It wold also be much more useful to present this data on 2 graphs, one showing the CR of all concentrations and the control on one graph, the other all IE, as the differences between them would be much clearer. If the weight loss measurements were conducted in triplicate then error bars should also be included. In section 3.3 it is mentioned that: 'The insignificant reduction of surface coverage implies that the protection performance of BTO is temperature-independent. Hence, BTO works as an effective inhibitor in the range of temperature investigated.' However a reduction in IE from around 97 to 92% seems significant, references here to support the statement are needed. Figure 3 should not be smoothed.
 Section 3.4: It is stated that: 'The adsorption isotherm subject explains the interactions....' An adsorption isotherm calculation only models the interactions at the surface, so a word like 'indicates' would be more appropriate than 'explains'. Again, since Figure 4 is from CR data it should include error bars so an appropriate judgement of the fit to a Langmuir model can be made.
Section 3.5:  Delta E is compared to molecules previously modeled by the same group only, and while it does seem promising, how does it compare to a wider range of molecules from other groups?
The sentence: 'As per the hard–soft acid–base principle, the soft molecule has a lesser energy gap and higher basicity than the hard one, and conversely [35,36].' Does not make sense, please re-write. Also, the statement: 'As shown in Table 1, N increases with the growth of the number of inhibitor molecules, which confirms the significant efficiency.' Does not make sense as Table 1 only shows one set of data, not any changes in N or number of inhibitor molecules.
Section 3.6: How were these values calculated?
Conclusion: This mostly sums up the work well, although some more detail in point 8 to support statements like: 'The calculation results demonstrate the tested inhibitor is considered a promising and important corrosion inhibitor.' and 'The obtained parameters support the validity of the quantum chemical approach used in this study. According to quantum chemical calculations, the examined inhibitor has the strongest tendency to adsorb strongly onto the metal surface.' For example the examined inhibitor has the strongest affinity to adsorb compared to what?
References: There are a number of self citations that are inappropriate. References 10 and 11 are used for the corrosion rate and inhibition efficiency equations and refer to studies by the group that just used them. Unless these studies were influential in establishing these calculations they are not needed. Similarly, references 27-29 are references to back up the statement that a delta G of greater than 40 indicates chemisorption, however these references are just other studies and do not establish this fact. Reference 30 is used to explain that DFT saves time and is not needed and reference 31 is used to reference what HOMO and LUMO are, again unless this study established the technique it is not appropriate and if references are needed it should be to a source that established the calculations.

Author Response

Dear Sir, 

Thank you for your useful comments and suggestions, all have been done point by point, please see the revised manuscript and the attached file.

Thank you

Best regards

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The paper can  be published.